162 replies to this topic

[Dan]

Hold on, it's not the end of the story by a long way. I'm surprised you managed to avoid using the 'Topic Closed' smiley to go along with that.

Think about this from our point of view for a minute. The evidence you have provided (ignoring the evidence that this tap actually exists for a moment which is a seperate issue) comes from a very old manual. This is why I asked you whether the manual in question describes the coil spring clutch or the diaphragm spring clutch. What date is the manual? You may not be aware that cranks, primary gears and flywheel bolts were all changed in 1963. The flywheel bolt from a 1959 - 62 car is not compatible with the crank from a later car and I've never known why but it may be due to the thread. Officially the only change was the primary gear design though. My earliest BMC manual is dated 1969 and doesn't describe this thread (I have an Autobook from 1968 that lists the coil spring clutch but it doesn't describe the thread either), giving me the impression that after the crank change the thread became a more recognised standard. Especially considering that between the date of the original design of the Mini and the redesign of the primary gear the Whitworth thread was dropped by British Standards. Not knowing the date of your blue book makes this more than a little uncertain still but its a working theory. Bearing in mind that several well known and respected engine builders use a certain thread makes it a little more believable than a very old manual published about the time that this thread may have been redesigned.

The real oddity is that one or other of these taps must be wrong. You haven't found a problem using your Whitworth tap and others have had no problem with a UNS tap. Despite the fact that you seem to be assuming that everyone is shaving a lot of swarf off their threads and simply not noticing I tend to assume that isn't the case for either you or anyone else. The difference is not simply a 5 degree change in cut angle, because the thread pitch of each is the same at 16 TPI the change in angle will make the thread depth very different. Since the major diameter is the same at 5/8" the extra depth of the thread will mean the Whitworth tap isn't actually touching anything other than the peak of the thread inside the crank if the thread is UNS. It wouldn't be capable of cutting anything. If it were the other way around however there would be a real problem with lots of material being removed. The problem would be reversed when dealing with the male thread on the bolt. The simple way to prove this is with a thread gauge and a selection of cranks and flywheel bolts from either side of 1963 but personally I don't have all that to hand. Or with a die of one thread or the other being run down a flywheel bolt but I doubt anybody has a die like that and with a split die that wouldn't really be proof anyway.

This is what you call a debate. That is where people have differing opinions and use structured arguments to back them up hoping to find a resolution. No evidence is ever impirical, especially when it's getting on towards 50 years old. I don't believe anyone here sets themselves up as an expert, we all learn from one another. Some know more than others but we all learn. Frankly the 'in-line engine debate' was nothing more than farcical. If you can't accept that words can have more than one meaning, especially when dealing with a language used by so many different nations you are in for a lot of dissapointment in life.

Edited by Dan, 28 March 2009 - 08:34 PM.

[Nightrain]

Well it is finished, as far as Im concerned. But it seems you don't want to have anybody contradicting your assumption that it is a UNS tap. Im very sorry if you don't want to believe somebody's trying to help you, so I'll give it another go.
1. The crank thread wasn't changed when the clutch was !
2. The A series engine was designed long before the UNS format came into been. BMC wouldn't have re-tooled expensive, just remember who where talking about here.
3. The blue manual isn't at home, so just for you I've had a quick search of a few other original workshop manuals. Do you own the Red 'MINI Workshop Manual, A BMC Service Publication' printed 2/68 ? Longtime after the spring clutch was introduced ! Look at page A20 Section A.31 if you do.
4. When someone wants a crank thread cleaning up, they take it down there local engineering shop. They measure the thread and cant quite match it. But a UNS tap is pretty close. So what do you think they do ? Buy another expensive piece of kit they will in all probability never use again or do they stick the uns tap down it.
5. As far as Im concerned this isn't a debate and I am trying not to be funny or clever but I have proved this without a shadow of doubt myself and discussed it on various forums and with lots of different people & every single one of them has had to concede that it is in fact a 5/8" Whitworth Fine thread.
6. You said 'ignoring the evidence that this tap actually exists for a moment which is a seperate issue' what the hell is that about are you saying I knocked it up quickly out of a scrap piece of steel on the lathe and stamped it up myself ?

[bigmotherwhale]

i just went into my garage and found a 5/8 whitworth tap and it had a course thread so there must be a whitworth fine, dont know if that helps at all, i thought i had a 5/8 whitworth fine but it turned out to be 5/8 bsf

[Dan]

I am determined to try and keep a discussion going here because I really want this answered. Believe me I know all about people who won't listen when you are trying to help them but that's not what's going on here. Please don't take everything so personally. The only reason I hold an opinion different from yours is that you are the only person I have ever heard this from. Really the only one. What you are saying goes against several things that I took to be facts and against the advice of several respected engine builders. Please remember that I don't know who you are or anything about you, I have no reason to either believe or disbelieve anything you might say just based on your word but one voice against a crowd is always going to suffer doubt. To answer the points you have made:

1: If that's the case why are there two different part numbers for crank bolts before and after '63? To all intents the bolts look generally the same.

2: Obviously the A series was designed long before Mini came along but it didn't have a tapered tail crank with a thread in it until the Mini was created. Re-tooling to change the threadform would be a negligable cost during re-tooling for the dry primary gear, especially since threading tools are periodically replaced anyway.

3: No my manual is from '69 as I said but I looked it up using your reference and the paragraph is indeed there, I apologise. I don't know why I didn't see it before.

4: No decent engineer would ever do that. Especially on a high load, critical torque thread like this.

6: That means nothing more or less than you having this tap doesn't mean it properly matches the thread any more than GW having a UNS tap means that his will fit. Please don't take everything so personally.

And my main point remains:

How do you account for the UNS tap fitting the thread without removing large amounts of material? As I said above the Whit tap will clear the UNS thread but a UNS tap would make a real mess of a Whit thread.

Again please don't take any of this personally. I and I'm sure several others would like you to respond to this because we all want to know but If you feel you don't want to that's fine. You've got me interested now though and if we can't settle this on the forum I will start asking around other sources. I know you feel there isn't even a discussion to answer here because you are certain of your facts but bear in mind that others feel exactly the same about their opinion. If you've been through this on other forums before then you must be getting bored of it but it is an important point. This is what forums are for.

<I've had to write this again because the damn computer lost it all when I went to send it before and I've probably missed something out but you get the general idea>

[Nightrain]

I am determined to try and keep a discussion going here because I really want this answered. Believe me I know all about people who won't listen when you are trying to help them but that's not what's going on here. Please don't take everything so personally. The only reason I hold an opinion different from yours is that you are the only person I have ever heard this from. Really the only one. What you are saying goes against several things that I took to be facts and against the advice of several respected engine builders. Please remember that I don't know who you are or anything about you, I have no reason to either believe or disbelieve anything you might say just based on your word but one voice against a crowd is always going to suffer doubt. To answer the points you have made:

1: If that's the case why are there two different part numbers for crank bolts before and after '63? To all intents the bolts look generally the same.

2: Obviously the A series was designed long before Mini came along but it didn't have a tapered tail crank with a thread in it until the Mini was created. Re-tooling to change the threadform would be a negligable cost during re-tooling for the dry primary gear, especially since threading tools are periodically replaced anyway.

3: No my manual is from '69 as I said but I looked it up using your reference and the paragraph is indeed there, I apologise. I don't know why I didn't see it before.

4: No decent engineer would ever do that. Especially on a high load, critical torque thread like this.

6: That means nothing more or less than you having this tap doesn't mean it properly matches the thread any more than GW having a UNS tap means that his will fit. Please don't take everything so personally.

And my main point remains:

How do you account for the UNS tap fitting the thread without removing large amounts of material? As I said above the Whit tap will clear the UNS thread but a UNS tap would make a real mess of a Whit thread.

Again please don't take any of this personally. I and I'm sure several others would like you to respond to this because we all want to know but If you feel you don't want to that's fine. You've got me interested now though and if we can't settle this on the forum I will start asking around other sources. I know you feel there isn't even a discussion to answer here because you are certain of your facts but bear in mind that others feel exactly the same about their opinion. If you've been through this on other forums before then you must be getting bored of it but it is an important point. This is what forums are for.

<I've had to write this again because the damn computer lost it all when I went to send it before and I've probably missed something out but you get the general idea>

1. Seem to remember the spring clutch had a slightly different size head to the 5/8' WF bolt.

2. Didn't they have a crank damper either ? Same thread. So stands to reason they'd use the same tooling !

3. So you've seen the text in the manual, seen the pic of the tap and still you doubt what I'm saying........

4. Seen it done or rather seen the taps some specialist engine builders use, which is the WRONG size ie.5/8" UNS.

5. What happened to five ?

6. You probably haven't even seen either tap or how they fit yet, your prepared to question everything I've said. Please don't take this personally. But isn't that the same as saying I'm talking *poop poop* ?

[Ethel]

I always thought BSF was the corresponding fine version of BSW? I too have never heard of Whitworth fine, not that it means anything Without any specifications it does make it harder to judge for sure what's on the crank nose.

There seems to be a consensus that it's 16tpi pitch and the same nominal major diameter. Both taps will have radiused peaks as they're taps but the UNS should have flat root to produce a truncated peak female thread. By my reckoning if the actual major diameter is near enough the same then the Whitworth profile would produce steeper & deeper valleys - requiring a smaller tap drill. A UNS tap would need a bigger pilot hole and would dig out more metal to produce wider valleys. Consequently if you had a Whitworth hole a UNS tap would remove metal as surely as erosion removes rock from real peaks to leave less steep and less deep valleys. I guess if we wanted a definitive answer a hole could be tapped with each thread then retapped to the other pattern and the result compared to what happens when the tap is passed down the crank tail.

Or you could just measure the minor diameter of the crank hole 'n see if it's within 0.5710 to 0.5570 - the specs for 5/8-16UNS, any smaller 'n it looks like it's not.

[MRA]

The Exact size is 5/8" WF (Whitworth Fine)

It is not a Whitworth thread which has a pitch angle of 55 degrees UNS as for all UN threads is 60 degrees )

[MRA]

i just went into my garage and found a 5/8 whitworth tap and it had a course thread so there must be a whitworth fine, dont know if that helps at all, i thought i had a 5/8 whitworth fine but it turned out to be 5/8 bsf

Whitworth fine ! sorry guys this never existed as a BSI name it may have been used by garages as a "nickname" for what should be calle BSF or British Standard Fine.... still 60 degrees, I have had the crank tail on a shadow graph and it is definately 60 degrees.

[MRA]

BS84 states that 5/8" BSF is 14tpi Fine - or BSW is 11tpi I would be interested in seeing a "whitworth" 16tpi and to what BS spec its too ?

[Guess-Works.com]

I don't want to emphasise the importance of this too much, but this is a revelation to many, if not all of us..

Ok this is a bit strong, but at one point everyone thought the world was flat ( some still do, but we'll leave them in their caves ), but this was "proved" not to be the case...

Here we have documented evidence that the thread in the crank is not the "accepted fact" that it's a 5/8 16UNS form, but a Whitworth form..

After searching pretty much all the doc I have on Mini's I've found said same extract in the 'Orange' workshop manual AKD 4935 (9th edition) printed in 1976...

If I'm going to get some taps made, then I need to know what form to get them made to.... and at this moment in time, I'm leaning towards the Whitworth form thread...

The question is, what thread is being put down billet / special order cranks ??

[Nightrain]

The Exact size is 5/8" WF (Whitworth Fine)

It is not a Whitworth thread which has a pitch angle of 55 degrees UNS as for all UN threads is 60 degrees )

i just went into my garage and found a 5/8 whitworth tap and it had a course thread so there must be a whitworth fine, dont know if that helps at all, i thought i had a 5/8 whitworth fine but it turned out to be 5/8 bsf

Whitworth fine ! sorry guys this never existed as a BSI name it may have been used by garages as a "nickname" for what should be calle BSF or British Standard Fine.... still 60 degrees, I have had the crank tail on a shadow graph and it is definately 60 degrees.

BS84 states that 5/8" BSF is 14tpi Fine - or BSW is 11tpi I would be interested in seeing a "whitworth" 16tpi and to what BS spec its too ?

Just what this thread need's, late entry from another expert lol FFS read all the thread and have a look at the pic I uploaded !

[bigmotherwhale]

[/quote]
Whitworth fine ! sorry guys this never existed as a BSI name it may have been used by garages as a "nickname" for what should be calle BSF or British Standard Fine.... still 60 degrees, I have had the crank tail on a shadow graph and it is definately 60 degrees.
[/quote]

this is clearly wrong! where did you get this information?, i have a BSF tap in my garage it it nowhere near the size of a crank thread, i have both of them side by side im 100%, whatever it is its not BSF

[MRA]

Hold on, it's not the end of the story by a long way. I'm surprised you managed to avoid using the 'Topic Closed' smiley to go along with that.

Think about this from our point of view for a minute. The evidence you have provided (ignoring the evidence that this tap actually exists for a moment which is a seperate issue) comes from a very old manual. This is why I asked you whether the manual in question describes the coil spring clutch or the diaphragm spring clutch. What date is the manual? You may not be aware that cranks, primary gears and flywheel bolts were all changed in 1963. The flywheel bolt from a 1959 - 62 car is not compatible with the crank from a later car and I've never known why but it may be due to the thread. Officially the only change was the primary gear design though. My earliest BMC manual is dated 1969 and doesn't describe this thread (I have an Autobook from 1968 that lists the coil spring clutch but it doesn't describe the thread either), giving me the impression that after the crank change the thread became a more recognised standard. Especially considering that between the date of the original design of the Mini and the redesign of the primary gear the Whitworth thread was dropped by British Standards. Not knowing the date of your blue book makes this more than a little uncertain still but its a working theory. Bearing in mind that several well known and respected engine builders use a certain thread makes it a little more believable than a very old manual published about the time that this thread may have been redesigned.

The real oddity is that one or other of these taps must be wrong. You haven't found a problem using your Whitworth tap and others have had no problem with a UNS tap. Despite the fact that you seem to be assuming that everyone is shaving a lot of swarf off their threads and simply not noticing I tend to assume that isn't the case for either you or anyone else. The difference is not simply a 5 degree change in cut angle, because the thread pitch of each is the same at 16 TPI the change in angle will make the thread depth very different. Since the major diameter is the same at 5/8" the extra depth of the thread will mean the Whitworth tap isn't actually touching anything other than the peak of the thread inside the crank if the thread is UNS. It wouldn't be capable of cutting anything. If it were the other way around however there would be a real problem with lots of material being removed. The problem would be reversed when dealing with the male thread on the bolt. The simple way to prove this is with a thread gauge and a selection of cranks and flywheel bolts from either side of 1963 but personally I don't have all that to hand. Or with a die of one thread or the other being run down a flywheel bolt but I doubt anybody has a die like that and with a split die that wouldn't really be proof anyway.

This is what you call a debate. That is where people have differing opinions and use structured arguments to back them up hoping to find a resolution. No evidence is ever impirical, especially when it's getting on towards 50 years old. I don't believe anyone here sets themselves up as an expert, we all learn from one another. Some know more than others but we all learn. Frankly the 'in-line engine debate' was nothing more than farcical. If you can't accept that words can have more than one meaning, especially when dealing with a language used by so many different nations you are in for a lot of dissapointment in life.

Lets just suppose there are two thread forms used on the Mini crank, the main reason why you would NOT notice that either a Whit 16 or a UNS 16 is wrong is that there has to be a clearance between the mating flanks of the male to female thread, this small "gap" and the equally small difference between both forms (ie, 55 to 60 degrees) just would not be noticed...... This does not make either right... the correct tap is the correct tap nothing more and nothing less !

Edited by mra-minis.co.uk, 29 March 2009 - 10:27 AM.

[bigmotherwhale]

thats irrelevant, we are trying to find what it is, not what will work we know UNS will work as it has been used before, and it wouldnt suprise me if rover also used UNS it becuse it was "close enough" too
why doesnt someoene mail KAD and ask them what thread they use on their EN24 hardened flywheel bolt?

[MRA]

The Exact size is 5/8" WF (Whitworth Fine)

It is not a Whitworth thread which has a pitch angle of 55 degrees UNS as for all UN threads is 60 degrees )

i just went into my garage and found a 5/8 whitworth tap and it had a course thread so there must be a whitworth fine, dont know if that helps at all, i thought i had a 5/8 whitworth fine but it turned out to be 5/8 bsf

Whitworth fine ! sorry guys this never existed as a BSI name it may have been used by garages as a "nickname" for what should be calle BSF or British Standard Fine.... still 60 degrees, I have had the crank tail on a shadow graph and it is definately 60 degrees.

BS84 states that 5/8" BSF is 14tpi Fine - or BSW is 11tpi I would be interested in seeing a "whitworth" 16tpi and to what BS spec its too ?

Just what this thread need's, late entry from another expert lol FFS read all the thread and have a look at the pic I uploaded !

Whitworth fine is still not a recognised thread form, look in the BSI book, BS84....... What is recognised is the Whitworth form especially the 55 degree flank angle (the root and crest radius are also important). so I can make a tap to Whitworth form say.... 17mm 11.25 tpi with a Whitworth thread form does not make it a whitworth "recognised" thread ....... any size, pitch and thread form can be made....

How do you explain my shadowgraph analysis ??

Also I fail to see how the tap that someone recommended earlier (5/8 UNF) would work ??

Edited by mra-minis.co.uk, 29 March 2009 - 10:53 AM.